More than 15 million elderly Americans slowly lose their eyesight due to age-related macular degeneration: an accumulation of inflammation-related protein and fat beneath the center of the retina that slowly destroys it. The disorder runs in families, but the gene responsible had eluded scientists. In March three separate teams announced that they had zeroed in on a DNA sequence on chromosome 1 that carries the gene for complement factor H, a protein involved in regulating inflammation. A mutation in this gene may account for about half the cases of macular degeneration in the United States.
This genetic culprit was revealed by a second and little-heralded phase in the Human Genome Project, and it comes five years after a rough draft of the entire human genome was announced. Touted as the key to deciphering the genetic book of life, that initial sequence has proved most useful for finding or confirming genetic mutations that cause rare diseases such as Tay-Sachs disease and Huntington’s. These alterations are relatively easy to identify because they can be traced and isolated in families with a history of the disease. Finding genetic clues to common diseases is much more difficult because many genes—as well as lifestyle and environmental exposures—may be involved. So rather than search the entire genome for genes related to common cancers, heart disease, asthma, and diabetes, scientists have turned to detecting inherited variations in the genomes of different populations and how they may be linked to disease vulnerability.
